The present invention generally relates to battery packs and more specifically to a battery pack for supplying power to a tool.
Various electric devices utilize batteries for the supply of operating power. These devices include portable tools which are frequently powered by direct current (DC) sources, such as rechargeable batteries. Such tools include drills and power screw drivers and typically do not require very high voltages. Portable tools that are powered by batteries frequently contain those batteries within the tool's structure. Batteries contained in this manner provide power only to that tool.
Other electric tools have been powered directly from an alternating current (AC) source. For example, many electric yard tools are powered directly from an AC source such as that provided by a standard household electrical outlet. A disadvantage of this type of tool is that it requires a connection (utilizing an electrical cord) to the electrical outlet due to the relatively high power requirements of such tools. As a user carries such a tool around a yard performing various tasks, the electrical cord can become entangled in various things (e.g., trees and/or various shrubbery, etc.) or cut by the tool itself.
To overcome these problems, yard tools have been constructed using gasoline-powered motors. Such gasoline-powered yard tools have been criticized for the air and noise pollution they cause. Battery-powered yard tools have not previously been considered due to the weight of the batteries that would be required to supply the amount of power needed to operate these yard tools.
Many prior art tools have employed a rheostat trigger that controls the voltage level applied by a DC or AC source to a motor of the tool. Some prior art tools have utilized a pulse width modulated waveform to supply power to a motor of the tool. In some of those devices, the width of the pulse width modulated waveform has been varied based upon an output voltage of a battery that supplies power to the device. In other devices, the duty cycle of a pulse width modulated waveform has been varied based upon a trigger signal. Many of these tools have included batteries within the tool's structure or alternatively have been powered by an AC source.